Activation Mechanisms of Natural Fractures Induced by Inter-Fracture Stress Interference

Natural fractures are extensively developed in unconventional reservoirs, and their effective activation is pivotal for forming complex fracture networks. Investigating the activation mechanisms and influencing factors of natural fractures is thus crucial for enhancing hydrocarbon production. This study develops a hydraulic fracture propagation model using the Displacement Discontinuity Method (DDM), quantifying planar stress components (σxx, σyy, σxy) around propagating fractures through coupled mechanical analysis.By integrating the Mohr-Coulomb failure criterion, we establish a mechanical model for natural fracture activation, systematically investigating the effects of fracture dip angle and spatial positioning on shear-slip behavior. A ranking-based stress difference index (ΔS = Scrit − Sactual) was introduced to quantify the interaction between critical and actual shear stresses on the activation probability. The research results indicate that (1) the stress concentration effect is particularly pronounced in the central region of the fracture, with shear stress fluctuations gradually weakening as the distance increases.; (2) natural fractures are more easily activated when the fracture dip angle ranges between 40°and 70°; (3) when ΔS ≤ −6, the activation ratio can reach its maximum value. The findings of this study provide a theoretical foundation and practical guidance for fracture optimization and complex fracture network construction in unconventional reservoirs.